The objective of the proposed research is to study the organization of immunoglobulin (Ig) genes, their regulated expression through transcription, translation and the synthesis of Ig precursor to provide the two final products - circulating antibodies and the antigen-recognizing receptor on the surface of lymphoid cells. The L-chain precursor, which is the immediate product of mRNA translation, contains an N-terminal extra piece (19-29 residues long) which precedes the N-terminus of the mature protein. Our studies of Ig precursors have already provided new information on the structure of Ig genes, and have stimulated new ideas concerning the organization and controlled expression of the V- and C-genes. These include: 1) the V-gene may be larger than hitherto realized; 2) the possibility that three genes may control the synthesis of one Ig chain; 3) independent expression of the C-gene associated with translocation of the extra piece DNA (the presumed third gene) directly to the C-gene; 4) the marked hydrophobicity of the extra piece may favor interaction of the precursor with cell membranes such as the endoplasmic reticulum where it is cleaved to provide mature protein destined for secretion, and the plasma membrane to provide the antigen-recognizing receptor; 5) the enzyme(s) cleaving the extra piece may be involved in the regulation of Ig secretion; 6) a recognition pattern for the enzyme(s) cleaving the extra piece is indicated from some residues (Gly, Leu) constant in all Ig extra pieces studied; 7) Frequency Distribution Analysis of Amino Acids (FDA) is an approach currently being developed to study and characterize the total repertoire of heterogeneous V-genes expressed in normal spleen and other organs. We plan to continue investigation of the structure-function relationship of the Ig precursor, and to extend the studies done on mouse myelomas to L- and H-chain of normal lymphocytes from mouse and other species.